1. Field of the Invention
The present invention relates to a crystallized glass and a method of manufacturing the same, for example, to a crystallized glass adapted for various kinds of materials which require a fine processing or a precision processing, e.g., material for electronic parts, material for a substrate for electronic parts, material for magnetic disk substrates, or the like.
2. Description of Related Art
A crystallized glass comprising .beta.-spodumene solid solution as the predominant crystal phase is used as a high-strength material because of its high mechanical strength and low expansion coefficient, and is also used for dishes which double as cooking utensils, a top plate for an electromagnetic cooking device and the like because the appearance thereof has a white colour and gives an impression of cleanliness and stains thereon easily come out. In the electronic industry, such a crystallized glass is used for a setter for burning for electronic parts and the like, an insulating protection tube for a heater, and the like. Recently, because a crystal having a length of about 1 .mu.m can be deposited, the crystallized glass is also used for material for electronic parts, and material for a substrate.
Such a crystallized glass comprising .beta.-spodumene solid solution as the predominant crystal phase is generally obtained by melting a raw glass, forming, and cooling the material, and then carrying out a heat-treatment for nucleation and by carrying out a subsequent heat-treatment for crystallization.
Japanese Patent Application Publication (Examined) No. Tokuko-Hei 1-57058 discloses a crystallized glass, the strength of which is improved by properly controlling growth of both .beta.-spodumene crystal and cristobalite crystal to deposit during crystallizing a raw glass. Japanese Patent Application Publication (Unexamined) No. Tokukai-Sho 58-49633 discloses a glass that contains fine crystal particles and has a greater mechanical strength and a lower coefficient of expansion, which is produced by combining F and As.sub.2 O.sub.3, which are necessary constituents for crystallization, with crystal nucleating agents. In addition, U.S. Pat. No. 4,192,665 teaches crystallized glass produced by crystallization of raw glass of composition: Li.sub.2 O--Al.sub.2 O.sub.3 --SiO.sub.2 --MgO--ZnO--TiO.sub.2 at a crystallization temperature lower than 1000.degree. C.
However, in those conventional crystallized glass of the above references, there have been some problems that because the raw glass is melted at a high temperature not less than about 1500.degree. C., clarification in melting tends to decrease. Also, both temperatures for nucleating and crystallization of the above products of crystallized glass are high, and in particular the crystallization temperatures are 900 to 1000.degree. C. so that coarse particles are likely to form in crystals to pose problems in quality. In addition, in crystallized glass which requires F as a necessary constituent, it has been disadvantageous that glass homogeneity is impaired because of evaporation of F upon melting.